With the increasing depletion of petroleum resources, there are needs for methods of decreasing the material costs and producing value-added products using heavy oils generated in the course of refining crude oils or using, as alternatives to crude oils, inexpensive heavy hydrocarbon oils such as bitumen. In order to actively address these environmental changes in the petroleum product fields, a variety of heavy oils are blended as semi-finished heavy oil products and thus utilized for fuel oils, ship oils and the like. Also, crude oils derived from various origins have been employed via blending. Since blending of hydrocarbon oils or crude oils is typically implemented in the oil refining fields, stabilized hydrocarbon oil blends have to be essentially produced.
However, such heavy oils and crude oils contain a considerable amount of asphaltenes, and thus stability thereof may become problematic upon blending. Individual heavy oils or crude oils are composed primarily of saturated hydrocarbons (saturates), aromatic hydrocarbons (aromatics), resins (mainly including alkyls and naphthenoaromatic hydrocarbons) and asphaltenes, wherein asphaltenes and maltenes (i.e., saturated hydrocarbons, aromatic hydrocarbons and resins) are linked in the form of micelles to form a colloidal system in a dispersion phase, and are thus stabilized.
In this regard, saturated hydrocarbons have the lowest polarity, and molecular weight, polarity and aromaticity are increased in the order of aromatic hydrocarbons, resins and asphaltenes. As such, asphaltenes are insoluble in n-heptane (C7 insoluble), and maltenes are soluble in n-heptane. Typically, asphaltene content is measured by ASTM D 6560-00. The exemplary properties of asphaltenes are shown in Table 1 below.
TABLE 1PropertiesH/C ratio0.8-1.4MwMonomer: about 500-1000Micelle: 1000-5000Heteroatom contentSulfur (S): 0.5-10 wt %Nitrogen (N): 0.6-2.6 wt %Oxygen (O): 0.3-4.8 wt %Contained metalNickel, Vanadium, Iron, etc.
Among the four types of hydrocarbons as above, asphaltenes having the highest C/H ratio are configured such that condensed polycyclic aromatics are stacked in the form of a multilayer, and are sensitive to thermal or chemical reactions or blending. Hence, asphaltenes are regarded as an important factor that affects storage stability of the blend. When storage stability is good, asphaltenes may adsorb resins from maltenes to form micelles, and are three-dimensionally (spatially) stabilized in an adsorption equilibrium state and do not settle in oils.
However, when resins are separated from asphaltenes due to deviation of adsorption equilibrium via the blending of different oils, asphaltenes may be settled (precipitated) (referred to as “dry sludge” or “total sediments”).
Even if the particular oils exhibit stabilized behaviors when they are individually present, the stability of asphaltenes therein may be significantly influenced by the changes of conditions such as blending with different types of oils.
When heavy oils or heavy oil and crude oil are blended so as to be utilized as fuel oils or ship oils or when various crude oils are blended so as to be transported via pipelines or to serve as fuel oils, the precipitation of asphaltenes arising from blending of hydrocarbon oils may cause serious problems including nozzle plugging in combustion devices, fouling and coking, and clogging of pipelines.
In this regard, methods of pre-checking stability problems of the hydrocarbon oils or crude oils have been devised in the pertinent art. For example, SPOT testing according to ASTM D 4740-02 is used to evaluate storage stability by qualitatively measuring cleanliness of oils and compatibility (miscibility) of components (semi-finished products) to be blended, and HFT (Hot Filtration Test) according to ASTM D 4870-99 is a quantitative method for measuring the total precipitate in oils.
Moreover, a method of evaluating the extent of potential deterioration of stability by measuring the amount of saturated hydrocarbons relative to aromatic compounds (which is referred to as “SARA”) is known. In addition, the use of sensitive neutron scattering to measure the presence and amount of asphaltene aggregates in petroleum oil blends (U.S. Pat. No. 7,029,570) is known in the art.
Although such methods are useful for checking the stability of the blends in part, they have technical limitations, for example, how to blend a plurality of hydrocarbon oils without precipitation of asphaltenes cannot be predicted in advance.
With the aim of solving such technical limitations, a method of preparing a stabilized blend of two or more petroleum oils using new parameters including IN (Insolubility Number) and SBN (Solubility Blending Number) is disclosed (U.S. Pat. No. 5,871,634). Also, a method of predicting stability of an oil blend using parameters such as critical solvent power and solvent power for individual oils is disclosed (U.S. Pat. No. 7,618,822).
However, the aforementioned techniques involve comparatively complicated calculations and procedures to determine the related parameters, and thus a method of preparing a stabilized hydrocarbon oil blend using a prediction model that is quick, easy and reliable is still needed in the art.